Glomerulus development in medaka and zebrafish pronephros in comparison to mouse and rat metanephros.

A1-B5: Pronephric glomerulus development in 3 to 6 dpf medaka (A1-A5) and 34 hpf to 4 dpf zebrafish (B1-B5) by JB4 cross sections stained by hematoxylin and eosin. The glomerular primordium of medaka exhibited a C-shaped epithelial layer (A2, A3), which is similar to the mouse and rat S-shaped body stage (C3, D3), unlike in zebrafish (B2). The C-shaped primordium contained a characteristic balloon-like or sinusoidal capillary. The paired pronephric glomerulus was fused at the midline to form a glomerulus in zebrafish (B3), but remained separated into two parts by the interposition of an interglomerular mesangium in medaka (arrowheads in A2-A5). C1-D5: Metanephric glomerulus development in rat epoxy resin sections stained by toluidine blue (C1-C5) and in mouse E18.5 kidney sections stained with H&E (D1-D5). Cross section of rat and mouse metanephros shows renal vesicle (C1, D1), comma-shaped body (C2, D2), S-shaped body at (C3, D3), capillary loop at (C4, D4), and maturing glomerulus (C5, D5). Rat vascular cleft in C2 (arrowhead) and primitive podocyte layer in C3 (asterisk). Mouse vascular cleft in D2 and D3 (arrowheads). Scale bars = 10 μm.

Temporal specification of the three glomerular components during glomerular development in zebrafish.

A1-A4: wt1a mRNA is expressed in the forming glomerulus from 34 hpf to 4 dpf. Cross sections show wt1a-positive podocyte layers of the paired glomeruli at 34 hpf (A1). Unlike medaka, zebrafish wt1a-positive podocytes are merged at 2 dpf (A2). B1-B4: Glomerular capillaries are detected by AP stain. At 34 hpf, the flattened nephron primordia show proximity to the dorsal aorta (B1). Glomerular capillaries are found at 2 dpf (B2). Dorsal aorta (arrows in B1-B4). C1-C4: GBM and mesangial matrix are detected by PAM stain. The paired glomeruli fuse at the midline and the interglomerular mesangium is not formed (C2-C4). Scale bars = 10 μm.

The progression of podocyte differentiation visualized by Podocalyxin immunostaining.

A1-A3: Cross sections of rat metanephric glomeruli. Throughout the rat metanephric glomeruli development, Podocalyxin is mainly localized at the apical membrane of podocytes. At the S-shaped body stage, Podocalyxin marks the apical membrane of the individual podocytes in a cap-shaped pattern (arrowheads in A1). By early capillary loop stage, Podocalyxin localizes in a U-shaped pattern in the individual podocytes (arrowheads A2). By the maturing glomerulus stage, Podocalyxin staining is detected along the entire surface of podocytes (A3). B1-B3: Cross sections of medaka pronephric glomeruli. Podocalyxin immunostaining is detected in the individual podocytes as a U-shaped pattern at 3 and 4 dpf (B1, B2). At 7 dpf, Podocalyxin staining is detected along the entire surface of podocytes (B3). Asterisks indicate blood cells in dorsal aorta. C1-C3: Cross sections of zebrafish pronephric glomeruli. At 34 hpf, Podocalyxin marks the apical membrane of individual podocytes at 34 hpf (C1). By 2 dpf (C2) and 5 dpf (C3), Podocalyxin immunostaining is expressed along entire surface of podocytes. Scale bars = 10 μm.